In part d , the diagram shows the relative size of the atoms, and the bonds are represented by the touching of the atoms. The polar covalent bonding of hydrogen and oxygen in water results in interesting behavior, suc. Water is attracted by positive and by negative electrostatic forces because the liquid polar covalent water molecules are able to move around so they can orient themselves in the presence of an electrostatic force. Although we cannot see the individual molecules, we can infer from our observations that in the presence of a negative charge, water molecules turn so that their positive hydrogen poles face a negatively charged object.
The same would be true in the presence of a positively charged object; the water molecules turn so that the negative oxygen poles face the positive object.
See Fig. Polar covalent molecules exist whenever there is an asymmetry , or uneven distribution of electrons in a molecule. One or more of these asymmetric atoms pulls electrons more strongly than the other atoms. For example, the polar compound methyl alcohol has a negative pole made of carbon and hydrogen and a positive pole made of oxygen and hydrogen see Fig.
When molecules are symmetrical , however, the atoms pull equally on the electrons and the charge distribution is uniform. Symmetrical molecules are nonpolar. Because nonpolar molecules share their charges evenly, they do not react to electrostatic charges like water does. Covalent molecules made of only one type of atom, like hydrogen gas H2 , are nonpolar because the hydrogen atoms share their electrons equally.
Molecules made of more than one type of covalently bonded nonmetal atoms, like carbon dioxide gas CO2 , remain nonpolar if they are symmetrical or if their atoms have relatively equal pull. Even large compounds like hexane gasoline C6H14 , is symmetrical and nonpolar. Electrostatic charges do not seem to have much, if any, effect on nonpolar compounds. Further Investigations.
Activity: Water and Electrostatic Forces. Special Features:. Explain Show molecular model animations that illustrate why water molecules are attracted to each other. First Frame of the Animation Electrons are shared between atoms in a covalent bond. Remind students how the shared electrons in a water molecule are attracted to the protons in both the oxygen and the hydrogen atoms.
These attractions hold the atoms together. Water molecules are neutral. Be sure students realize that no protons or electrons are gained or lost. The water molecule has a total of 10 protons and 10 electrons 8 from the oxygen atom and 1 from each of the two hydrogen atoms. Since it has the same number of protons and electrons, the water molecule is neutral. Tell students that another way to see the difference in where the electrons are is by using the electron cloud model.
Unequal sharing of electrons makes water a polar molecule. Tell students that the oxygen atom attracts electrons a little more strongly than hydrogen does. So even though the electrons from each atom are attracted by both the oxygen and the hydrogen, the electrons are a bit more attracted to the oxygen. This means that electrons spend a bit more time at the oxygen end of the molecule. This makes the oxygen end of the molecule slightly negative.
Since the electrons are not near the hydrogen end as much, that end is slightly positive. When a covalently bonded molecule has more electrons in one area than another, it is called a polar molecule.
The electron cloud model can show an unequal sharing of electrons. Point out that the electron cloud around the oxygen is darker than the electron cloud around the hydrogen. This shows that electrons are more attracted to the oxygen end of the molecule than the hydrogen end, making the water molecule polar.
Tell students that this is another model of a water molecule. In this model, color is used to show the polar areas of the water molecule. The negative area near the oxygen atom is red, and the positive area near the hydrogen atoms is blue.
Ask students: What do you notice about the way water molecules orient themselves? The red oxygen area of one water molecule is near the blue hydrogen end of another water molecule. Why do water molecules attract one another like this? Since the oxygen end of a water molecule is slightly negative and the hydrogen end is slightly positive, it makes sense that water molecules attract one another.
Give each student an activity sheet. Show students that the bonds between atoms in a molecule are different from the polar attractions between molecules. The bonds within molecules and the polar attractions between molecules.
A single atom stays together because of the attraction between the positively charged protons and the negatively charged electrons. In a molecule, two or more atoms stay together because of the mutual attraction between the positively charged protons from one atom and the negatively charged electrons from the other atom. This causes the covalent or ionic bonding that holds atoms or ions together.
Two or more water molecules stay together because of the positive and negative parts of the molecules attracting each other. Have students mark the positive and negative areas on a water molecule by color-coding their Styrofoam ball models.
Repeat this for your other water molecule. Position your water molecules so that opposite charges are near each other. Ask students: How do your Styrofoam ball models of water molecules relate to the color-coded charge density model shown in the animation? The different colors show that water is a polar molecule. Because water molecules are polar, how do they arrange themselves in liquid water? The positive area of one water molecule is attracted to the negative area of another water molecule.
Explore Have students design a test to compare the rate of evaporation between water and alcohol. Ask students: Do you think a substance like water with polar molecules would evaporate faster or slower than a substance like alcohol with molecules that are not as polar? The Triangular Wave treatment technology takes advantage of this unique characteristic of water, a polar molecule.
Water is a Polar Molecule. Hydrogen Bonds in Water. Scale Control Mechanism. Enhanced Colloidal Charge. Operating Principles.
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